There are in the art a number of flexible guide wires used in medical applications. Exemplary such devices are shown in U.S. Pat. Nos. 3,545,390, 4,538,622, 4,619,274, 5,053,404, and 5,267,574, and in U.S. application Ser. No. 08/069,050 filed May 28, 1993, now U.S. Pat. No 5,606,979 and owned by the assignee of the present application, all of which are here incorporated by reference. Some such devices, including those shown in U.S. Pat. Nos. 4,538,622 and 5,052,404, include a flexible main spring of stainless steel having a short radiopaque (e.g., platinum, gold, tantalum, tungsten, iridium, rhenium) spring joined to its distal end. In others, such as those shown in U.S. Pat. Nos. 3,545,390 and 5,267,574, the entire spring is made of a material (e.g., platinum or a platinum/tungsten alloy, having a relative high radiopacity. Whether the spring is one-piece or two-piece, a central core, which also may be stainless steel, typically extends coaxially within the entire length of the spring and is connected, e.g., by brazing, to both the distal and proximal ends of the spring. When a two-piece spring is employed, the adjacent ends of the two pieces of the spring are generally brazed both to each other and to the central core of the guide wire assembly.
Medical devices in which an entire spring is made of a radiopaque material such as tungsten are expensive, and the material may have less desirable characteristics than does a material such as stainless steel. Making only a portion, e.g., the distal end portion, of the spring of a radiopaque material somewhat reduces material costs, but requires two or more springs rather than one, along with the additional manufacturing costs and procedures that are required to insure a secure construction.
There have been attempts to provide guide wires having a two-piece construction in which a single stainless steel coil extends all the way to the tip, but these attempts have proved to be somewhat unsatisfactory. Neither the stainless steel itself, nor a layer of gold or the like plated onto the coil, has been sufficiently radiopaque.
There remains a need for a less-expensive spring device that is sufficiently radiopaque, and particularly for a guide wire having a radiopaque distal end.